1. Field of the Invention
This invention relates generally to materials separator apparatus and is concerned more particularly with a materials separator having varying width magnetic means for segregating electrically conductive particles of various sizes from a stream of commingled materials.
2. Discussion of the Prior Art
In the recycling of waste material, solid municipal waste initially may be shredded by conventional means, such as a hammer mill, for example, which generally reduces the waste material to more manageable particles of non-uniform size. After shredding, the non-uniform size particles may be conducted to a conventional air classifier wherein the particles of light fraction material, such as paper, for example, are separated from the particles of heavy fraction material. The heavy fraction particles then may be conveyed in a stream, as by an endless belt, for example, to a magnetic separator of the conventional type which separates particles of ferromagnetic or highly magnetic material, such as iron, for example, from the stream. Thus, the stream emerging from the magnetic separator is substantially comprised of heavy fraction particles of nonferromagnetic material including dielectric material, such as glass, rubber, and plastic, for examples, and electrically conductive material, such as aluminum, silver, copper, zinc, and the like. Since the electrically conductive particles of nonferromagnetic material constitute a significant percentage of the value of recycled waste material, material separators of the prior art have been developed for segregating the electrically conductive particles of nonferromagnetic material from the stream of commingled materials.
For example, U.S. Pat. No. 4,003,830 granted to E. Schloemann and assigned to the assignee of this invention discloses a materials separator comprising a ramp having a low friction, sloped surface down which the particles of non-ferromagnetic material slide in a stream due to the force of gravity acting on the particles. The sloped surface of the ramp is made of non-magnetic material and overlies an alternating series of oppositely polarized magnets having respective magnetic poles of substantially uniform width disposed adjacent the sloped surface of the ramp. The magnetic poles are disposed substantially parallel to one another and extend transversely at a uniform oblique angle to the longitudinal centerline of the sloped surface. Consequently, there is established above the sloped surface a spatially alternating, steady-state array of juxtaposed, oppositely directed magnetic fields having substantially uniform widths. The fields also are disposed substantially parallel to one another and extend transversely at a uniform oblique angle to the longitudinal centerline of the sloped surface.
Thus, particles in the stream sliding down the sloped surface of the ramp pass sequentially through oppositely directed fields of the spatially alternating array established by the underlying magnets. The dielectric particles of non-ferromagnetic material in the stream are substantially unaffected by the magnetic fields and continue to travel generally linear paths down the sloped surface due to the force of gravity. However, the electrically conductive particles of nonferromagnetic material, when passing sequentially through the oppositely directed fields of the array, have respective eddy-currents induced therein. These eddy-currents coact with the magnetic fields to exert on the electrically conductive particles respective resultant forces having deflecting components which move the particles laterally out of the stream, in a uniform direction, while they are sliding longitudinally down the sloped surface of the ramp. As a result, the electrically conductive particles of nonferromagnetic material separate angularly from the stream of commingled materials and may be collected in suitably disposed containers at the lower end of the sloped surface.
While the described apparatus has been found satisfactory for separating a wide range of electrically conductive particle sizes, it is sometimes desirable to separate a still wider range of electrically conductive particle sizes from the stream, particularly particles of extremely small size.